S Plan 40x on BH-2 BHS Light field/Dark field

[thomas.schwarz]

Hello friends,

I am not sure if it was like this originally, or if it happened after, maybe, some oil got on my S Plan 40x, but now:
1) Dark field, although perfect in my 4x and 10x, shows some lighter shade of grey (background) in my 40x
2) In Brightfield, my 40x wont focus unless I drop the condenser to get more contrast, then it seems to focus OK

...I tried cleaning my 40x in the normal way with lens paper and lense cleaning spray. Assuming that it has either oil, dust or cleaning solution inside, it there any way to clean it better? Are there other potential reasons for the weird behavior?

[Hobbyst46]

Hello friends,

I am not sure if it was like this originally, or if it happened after, maybe, some oil got on my S Plan 40x, but now:
1) Dark field, although perfect in my 4x and 10x, shows some lighter shade of grey (background) in my 40x
2) In Brightfield, my 40x wont focus unless I drop the condenser to get more contrast, then it seems to focus OK

...I tried cleaning my 40x in the normal way with lens paper and lense cleaning spray. Assuming that it has either oil, dust or cleaning solution inside, it there any way to clean it better? Are there other potential reasons for the weird behavior?

If you are not sure whether there is still oil on the front element, try to check it under an eyepiece. Hold the eyepiece upside down to inspect the objective.
Two chemicals are useful for oil removal without damage to the objective: 1. Isopropanol (AKA IPA), 2. Light petroleum ("white benzine", "petrol ether") or octane/isooctane/heptane.
I would start with no 2. In any case, use sparingly, a small drop on a piece of KimWipe or Q-tip.

[thomas.schwarz]

Interesting... ...I did look at the objective with eyepiece in reverse, and it looks horrible, very scratched concave lense. I did try to clean with Aethanolum 96% (Alkohol) and at least dark field is back to black background. But still no sharp focus. But at least close to focus with condenser up. So some improvement. I will try the light benzine/isooctane next...

Thanks!

[Hobbyst46]

Interesting... ...I did look at the objective with eyepiece in reverse, and it looks horrible, very scratched concave lense. I did try to clean with Aethanolum 96% (Alkohol) and at least dark field is back to black background. But still no sharp focus. But at least close to focus with condenser up. So some improvement. I will try the light benzine/isooctane next...

Thanks!

Ethyl alcohol, AKA ethanol, 96% and even absolute, is a poor fat and oil remover.
Good luck!

[thomas.schwarz]

Right... ...so what I used now was "Nitro" it is some super powerful paint thinner. And the results...
1) when I look at the objective with the reverse eyepiece, it looks perfect, like some kind of space telescope mirror
2) when I use the objective in bright field it is very good if not perfect
3) but... ..still when I use it in dark field it is nowhere near as clear as my 10x.

Soon I will have my photo tube and I will update with photos. But until then, newbie question, does 40x in your experience work with dark field to produce well focused images? If yes, could you please attach one?

Thanks!

[thomas.schwarz]

funny, here is a top google result for 40x darkfield. So am I correct that 40x darkfield generally will no be very sharp?

https://images.app.goo.gl/SVneDBXNTwDzvvbH6

[viktor j nilsson]

I think you should be very careful with such strong solvents as paint thinner. You risk ruining your coatings, which can seriously affect image quality.
There is lot's to read about cleaning lenses here and in the Zeiss folder The Clean Microscope. You should be able to clean your lenses without using unncessarily aggressive solvents.

I find that Zeiss optical cleaner cleans many contaminants very well. And Zippo lighter fluid is a cheap source for petroleum ether that is easily accessible in most places.

Have you checked the back focal plane of your objective when set up for darkfield? Do you have a phase telescope? It sounds like you may be getting some light spill near the periphery of the rear aperture.

[Hobbyst46]

funny, here is a top google result for 40x darkfield. So am I correct that 40x darkfield generally will no be very sharp?

https://images.app.goo.gl/SVneDBXNTwDzvvbH6

Trying to answer this question and the previous one.

I regretfully do not own a BH2, yet with my little Zeiss I obtain very nice darkfield with the 40X0.75 objective and the darkfield position of the condenser, where the condenser (not the objective) is oiled to the slide with immersion oil. By "nice" I mean dark black background. If the specimen is flat and thin, it appears to be sharp as well. Otherwise, stacking must be done.

A Spyrogira alga is not thin enough for a perfectly focused image of the whole FOV. This indeed is what the last link you attached shows. The background is black, OK, and the lack of sharpness is due to very selective focusing on a spot (in my opinion). The depth of focus is not sufficient.

Side note: I would not use "Nitro" on any part of a microscope. I am not saying that it damaged yours, but paint thinners are very powerful solvents that can dissolve and soften both optical cements as well as paint layers.

[thomas.schwarz]

Have you checked the back focal plane of your objective when set up for darkfield? Do you have a phase telescope? It sounds like you may be getting some light spill near the periphery of the rear aperture.

No phase on microscope. What is the back focal plane of the objective? That sounds promisimg because the other objectives work fine....

Ok zippo for the future, no more nitro. Promise.

[viktor j nilsson]

Have you checked the back focal plane of your objective when set up for darkfield? Do you have a phase telescope? It sounds like you may be getting some light spill near the periphery of the rear aperture.

No phase on microscope. What is the back focal plane of the objective? That sounds promisimg because the other objectives work fine....

Ok zippo for the future, no more nitro. Promise.

A phase telescope is often used when setting up phase contrast to make sure that the illumination phase plate matches the phase ring at the rear focal plane of the objective. But a phase telescope is also useful for many other things. It is basically an eyepiece that can move up and down so as to focus at different depths along the optical axis. You can, for example, use it to check each opical group within an objective for defects or dirt.

In this case, you can use it to focus on the rear focal plane of your 40x objective when set up for darkfield to see if your darkfield stop is working as it should. When you look at the rear focal plane in DF, it should be all black. Outside the edges of the field, there should be a ring of light. This means that no light hits your objective "straight-on", the objective is only catching light that gets diffracted by the specimen.

You can pickup any kind of cheap phase telescope on eBay, they will all do a good enough job. And it will help you will learn a lot about microscope illumination techniques.

This is a good read about image and illumination conjugate planes - when you check the rear focal plane, you are inspecting the illumination light path:

https://www.microscopyu.com/microscopy- ... microscopy

[carlh6902]

Thomas,

What are you using to obtain darkfield? A simple patch stop, and likely even a dedicated dry darkfield condenser, will not give optimal results at 40x. A wet (oiled) darkfield condenser should work well.

Carl

[thomas.schwarz]

A-mazing.  Grasshopper is hopping.   First answers…  I have a BH-2 BHS with a UCD (Universal Condenser).  It is set up with DIC (NIC) prisms (20x, 40x, 100x), but I do not yet have the Intermediate Analyser Tube/DIC Prism above the objectives.  But I do have a UDA (Darkfield stop) installed in the UCD (there are total of 4 positions plus BF in the condenser). So I only use the UCD in bright field and dark field.  I do have the Phase Anuli for Phase Contrast if someone needs them, but they are not installed currently.

I actually did get the CT-5 Centering Telescope, I read through that amazing link about focal planes (thank you!) and now…  ...I need a step by step for " use it to focus on the rear focal plane of your 40x objective when set up for darkfield to see if your darkfield stop is working as it should".

Here is what I am doing now with a functioning 10x for reference

0) first off, I remove the eyepiece, and the CT-5 just sits lightly on top of the hole with about 1 MM of its body inside the hole.  Is that OK?   It does not slide in like a normal eyepiece...
1) Focus my 10x with darkfield, using the CT-5 (10x requires the CT-5 is 100% contracted, 4x requires that CT-5 is fully extended), so I know which focal plane I am starting with (specimen focal plane).  Good way to start the analysis?
2) Gradually make the CT-5 longer/shorter, this should move me to the next focal plane?  E.g. to the objective rear focal plane?

So the first question, does shortening the CT-5 raise the point in the conjugate planes that I am viewing and extending the CT-5 bring me lower into the microscope?

[thomas.schwarz]

Argh, what I just noticed, no idea if this makes a difference for BF/DF, but I imagine it will effect DIC, is that my 4x and my 10x are D Plan, my 40x and my 100x are S Plan. FYI I have a 20x coming in the mail that is surely S Plan.... ...so on the DIC front, it is not an issue because my DIC prisms are 20x, 40x, 100x, the objectives for which are all S Plan (whewwww....)

[thomas.schwarz]

OK so I think I answered my first question about the CT-5 telescope; simply by experimenting, I can see that as I shorten it I focus on things farther away, and as I lengthen it I move up the microscope (see things that are closer).

So back to the issue of this thread, I was able to focus on the UDA Dark field filter, and I think that you are right, that with the 4x and 10x it blocks the light well. BUt with the 40 x light comes up around it. Any tips on what/where to adjust the UCD to fix that? I am tried the centering mechanism, I believe that the condenser is centered correctly. I also noticed that there are two twistable nobs to the right on the installed UCD which have slots for a screw driver, no idea what those do... tipps?

FYI everything (objectives, trinocular, condenser, etc...) is relatively clean with zippo lighter fluid and without question, the 40x is the cleanest of all, so no issues there....

[Hobbyst46]

OK so I think I answered my first question about the CT-5 telescope; simply by experimenting, I can see that as I shorten it I focus on things farther away, and as I lengthen it I move up the microscope (see things that are closer).

So back to the issue of this thread, I was able to focus on the UDA Dark field filter, and I think that you are right, that with the 4x and 10x it blocks the light well. BUt with the 40 x light comes up around it. Any tips on what/where to adjust the UCD to fix that? I am tried the centering mechanism, I believe that the condenser is centered correctly. I also noticed that there are two twistable nobs to the right on the installed UCD which have slots for a screw driver, no idea what those do... tipps?

FYI everything (objectives, trinocular, condenser, etc...) is relatively clean with zippo lighter fluid and without question, the 40x is the cleanest of all, so no issues there....

From the BH-2 brochure, the UDA DF ring is compatible with some of the 40X objectives.
May I suggest that you place a drop of oil immersion between the condenser and the bottom surface of the slide, likely it will enhance the darkfield. Do not oil the objective to the coverslip.

[thomas.schwarz]

Well, I could not put any only on my condenser, it will drip down on to the turret where my DIC prisms are, no?

[Hobbyst46]

Well, I could not put any only on my condenser, it will drip down on to the turret where my DIC prisms are, no?

I meant, a single small drop on the top lens of the condenser. Once the condenser is raised to the proper position, the top lens is within a millimeter or less from the bottom of the slide, the oil will spread, not drip.

[thomas.schwarz]

Thanks Hobbyst46, also suggested by carlh6902, tried the oil on condensor, but no effect. Funny, you know my condensor, the Universal Condensor, is nothing like a normal condensor... ...the final lense is on an arm and can move in and out of the light path. Not sure why, but one reason it is on an arm, is to install and remove the condensor, the lense needs to bend to the side, like you duck your head when entering a room with a low ceiling.... ...and that lense is very, very concave, so the oil just sits in there and does not touch the slide....

I would also like to know more about the idea from @viktor j nilsson.... So I am definately "getting some light spill near the periphery of the rear aperture", what can I do about it? Just improve the condenser position? Other possible root causes and potential solutions? As for seeing only dark when I focus my CT-5 telescope on the focal plane behind the objective, actually, all objectives show beige, not black... and show their dust (40x is cleanest). I know it is objective dust, because when I turn objective (tighten/loosen) the dust spins accordingly. Could that be dust inside the objective? It is OK to open the objective to clean that (saw on youtube)? Back to the 40x, I can see that it is the one objective that has light coming in to the objective rear focal plane... it looks like rays of gold around that beige background....

So my take on this, after playing around with the condensor centering mechanisms a great deal, is that my UDA stop is perfectly sized for my 4x and 10x D Plan objectives. But my 40x S Plan objective has this "light spilling" problem with my UCD UDA stop. Any tipps? I think next, I might try a Phase anuli as darkfield stop, in the place of the UDA in my UCD. I have two of those that came with the UCD that look a lot like a darkfield stop, that I have not tried.

[Hobbyst46]

Thanks Hobbyst46, also suggested by carlh6902, tried the oil on condensor, but no effect. Funny, you know my condensor, the Universal Condensor, is nothing like a normal condensor... ...the final lense is on an arm and can move in and out of the light path. Not sure why, but one reason it is on an arm, is to install and remove the condensor, the lense needs to bend to the side, like you duck your head when entering a room with a low ceiling.... ...and that lense is very, very concave, so the oil just sits in there and does not touch the slide....
...
I think next, I might try a Phase anuli as darkfield stop, in the place of the UDA in my UCD. I have two of those that came with the UCD that look a lot like a darkfield stop, that I have not tried.

The front lens of the condenser can be switched in and out depending on the objective. For low NA objectives (the 4X possibly) the field of view will be brighter if the front lens is switched out. With high NA objectives the front lens should be swung in. So it goes with my Zeiss condenser so I believe the same goes for the BH-2.
If the lens is concave - sorry, do not know.

IMO, phase annuli will probably serve well with the 4X and 10X, not the 40X. Again, by analogy with the Zeiss equipment.

P.S. the table on page 13 of the BH-2 brochure, where the UCD condenser is described, says it clearly: the NA of the condenser is 0.9 with the front lens and 0.2 without it. This is to perform well with high and low NAs objectives, respectively.

[viktor j nilsson]

Yes, I'd be very surprised if a single darkfield stop performed OK with 4x, 10x and 40x objectives. Trying some of the phase inserts seems like a good idea. Glad you got the CT-5 telescope working, it'll help immensely for you to understand what's going on.

Also, I haven't used Olympus objectives myself, but I'd be surprised if the S plan/D plan issue would ever be a problem, especially if you aren't even planning on using the S SPlans for DIC.